Alkyl alkanolamines and their derivatives are widely used in the chemical industry. N,N-dimethylethanolamine (DMEA), N-methyl, N-ethylethanolamine and N,N-diethylethanolamine are representative dialkylalkanolamines which have multiple uses; for example, they are used in the production of pharmaceutical products; paints and coatings; textile auxiliaries; corrosion inhibitors; dyestuffs; and as curing agents for epoxy and polyamide resins. A specific pharmaceutical use for N,N-dimethylethanolamine is in the synthesis of procaine, a valuable local anesthetic and as an intermediate in the preparation of procaine penicillin G, an important antibiotic. N,N-dimethylethanolamine and N-methylethanolamine are also used in the synthesis of antihistamines (e.g. diphenylhydramine hydrochloride) for the symptomatic relief of allergies, such as hay fever as well as the common cold.
Currently N,N-dimethylethanolamine is mainly used in the manufacture of functional acrylate or methacrylates monomers. These monomers and their quaternized derivatives are widely used in the production of cationic polyacrylamides and other polymers for water treatment and paper making.
A known problem of alkanolamines, in general, and the dialkylalkanolamines, in particular, is that following fractional distillation of the alkanolamine crude reaction product they either are or become discolored. The sources of this color contamination may be from metals and metal compounds leached from the equipment used in the process of manufacture, or from conjugated and carbonyl containing organic compounds which are formed during the manufacturing process. Since the mechanism by which these color contaminants are formed varies from process to process and, also, from product to product, the successful decolorization process depends to a certain degree on the color source and contaminating by-product. Decolorization processes for some alkanolamines are not necessarily suited for others.
There have been many processes suggested for removing color from alkanolamines. One method commonly employed is hydrogenation. But, these hydrogenation processes also differ in terms of the process and product employed. Representative patents and articles illustrating hydrogenation processes for the decolorization of alkanolamines and the catalytic metals used therefor are as follows:
U.S. Pat. No. 6,291,715 B1 (2001) discloses the preparation of alkanolamines with improved color stability by treating the alkanolamine with hydrogen in the presence of a hydrogenation catalyst at elevated temperature. The catalysts include the metals Re, Ru, Rh, Os, Pd, Ir, Pt and Ag. These metals are carried on the supports alpha-aluminum oxide, zirconium oxide, titanium dioxide, and activated carbon. Pd on xcex3-alumina was used to decolorize triethanolamine but the reaction product turned pink.
JP 01-160,947 (1989) describes the purification of dialkylaminoethanols by the steps (a) removal of high boiling compounds, (b) treatment with hydrogen in the presence of hydrogenation catalyst, e.g., 5%Ru/C and (c) distillation.
EP 028,555 B1 (1988) teaches a process for the purification of N,N-dialkylaminoethanols by catalytic hydrogenation in heterogeneous phase wherein the catalyst contains a metal selected from group VIII of the periodic system, such as Ni, Co, Pt, Rh or Pd. These metals are carried on various supports such as alumina, pumice, kiesulguhr, and activated carbon.
U.S. Pat. No. 3,207,790 (1965) describes a process for improving the color quality of alkanolamines by the addition of a borohydride of an alkali metal to the alkanolamine. However, the presence of an auxiliary (stabilizer) for improving the color quality of alkanolamines can be undesirable in many important areas of application.
U.S. Pat. No. 5,847,221 (1998) discloses a process for decolorizing alkanolamines and alkyleneamines by treatment with a perfluorinated ion-exchange polymer in the acid form. As acknowledged in the background, various chemicals, Impurities often enter the production processes and manifest themselves in the form of color contamination.
U.S. Pat. No. 3,819,710 (1974) describes a process for improving color and color stability of ethanolamines by hydrogenation using selected catalysts and selected catalysts conditions. Useful catalysts for the process include Raney nickel, platinum, palladium or ruthenium.
This invention relates to an improvement in a process for effecting decolorization of an alkanolamine by subjecting the alkanolamine to hydrogenation in the presence of a hydrogenation catalyst. The improvement for removing color or by-products or both from a dialkylalkanolamine represented by the formula: 
wherein R and R1 are methyl, ethyl, or a mixture thereof, which comprises: utilizing a catalyst comprised of palladium carried on gamma alumina as the hydrogenation catalyst.
Significant advantages can be achieved by the process and these include:
an ability to selectively reduce some impurities critical for the main application of N,Nxe2x80x2-dimethylethanolamine (DMEA) while obtaining a high color stability;
an ability to minimize by-product formation produced during hydrogenation; and,
an ability to use a heterogeneous catalyst in the hydrogenation allowing for process advantages.